How many Mapper and Reducer will run if the input directory of the job is empty?

[DataFlair Team]

What will happen if in a Map-Reduce Job if there is no data/file in input directory ?

How many Mapper and Reducer will run in this case?

[DataFlair Team]

If input directory is empty, then no mappers or Reducer will run.
As a number of mappers depend upon the number of InputSplits, as no data no input splits hence no mappers.
Without any mapper, a number of the reducer is also 0.

If we try to run map/reduce job on Hadoop cluster without specifying any input file it will throw following exception:

java.io.IOException: No input paths specified in job

[DataFlair Team]

Since the number of mappers depends upon the Input-Splits which in turn depends on the data, no mappers will be running in this job.

And since the Reducer receives the input from mapper, hence no reducers will be running as well.
When trying to run this job with no files under the input directory specified, an error will occur saying :
java.io.IOException: No input paths specified in job

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